Gas turbine engines comprise a plurality of bladed rotors, each of which comprises a rotor, typically in the form of a disc, and a plurality of rotor blades circumferentially mounted around the radial periphery of the rotor. Each rotor blade has an aerofoil, a platform, a shank and a root. The rotor comprises a plurality of circumferentially spaced axially extending slots defined by radially extending posts. The root of each rotor blade is arranged to locate in a respective one of the axially extending slots. The roots of the rotor blades are generally fir tree or dovetail shaped and the axially extending slots are correspondingly shaped to receive the roots of the rotor blades. The engagement of the roots in the slots is sufficient to radially retain the blades when under centrifugal loading induced during rotation of the rotor.
The bladed rotor arrangement also comprises a plurality of lock plates arranged at either or both axial ends of the rotor to prevent the rotor blades moving axially relative to the rotor. The lock plates also act to restrict fluid flowing under the platform of the blades.
The radially outer ends of lock plates typically engage grooves provided in the radially inward facing surfaces of the blade platforms, or flanges extending therefrom. The radially inner ends of the lock plates engage circumferentially extending grooves in the rotor or slots defined by additional structural members such as so-called cover plates or and seal plates.
In the case of a turbine stage lock plate, the components are exposed to extreme temperatures and pressures, and high levels of centrifugal loading as the rotor spins. And of course, the lock plates are required to maintain the requisite functionality whilst withstanding these extreme forces placed on the components.
The lock plates are designed to be undersized in a cold build condition to allow for operational movement resulting from thermal expansion and centrifugal forces, and also to allow for manufacturing tolerances and build clearances.
Further, the centrifugal loading is ultimately carried by the blade platform grooves in which the radially outer edges of the lock plates are located. Thus, there is a general requirement to minimise the mass of the lock plates to help reduce the resultant parasitic loading on the blades and any other associated components.
The present invention seeks to provide an improved bladed rotor arrangement and associated lock plate.